The present invention relates to a friction welding apparatus and process, and more particularly, to an apparatus and process for friction welding of cylindrical joint parts using a respective receiving fixture for holding the joint parts and a device for confining a weld bead during a weld upsetting procedure. The process comprises steps in which the receiving fixtures, one of which is rotary-drivable about a rotational axis, are mutually displaceable along a direction of the rotational axis, and in which, during an upsetting procedure, the rotary-drivable receiving fixture are set in rotation, the joint parts are pressed together with the application of axial compression forces and are heated in the region of a bonding zone situated at adjacent end faces thereof, and in which the weld bead in the warm state, in the region of origin of the welding burr, is confined during the weld upsetting procedure.
In a known process of the type stated in the introduction of Wichelhaus/Gruenauer "Preconditions Prospects for Friction Butt-Welding", German Journal "MM Maschinenmarkt", No. 70/1975, Vogel-Verlag Wurzburg, expulsion of plastic material from the torsional-flow zone during a welding operation produces, at the junction point, a welding burr. By virtue of faster cooling, the burr is generally harder than the welding zone which has a fine-grained recrystallization structure and therefore favorable strength and toughness characteristics. Nevertheless, the welding burr in the known process is twisted off, while still warm, immediately after the welding operation is completed.
The burrs which are formed in the friction welding disrupt the usability of the structural part having the weld joint. A mechanical removal (machine-cutting process), such as in the known case, is very complex, however, because the burr has a very high strength, by virtue of this welding process.
In the known process, the actual welding or upsetting procedure is preceded by a joint-part preparation procedure which relinquishes, however, an abutting-face preparation in the case of virtually plane-parallel severance cuts and, with respect to thin-walled pipes, is more or less restricted to measures to keep the axial slip as low as possible, but otherwise simply to remove coatings and impurities from the abutting faces.
It is further known from U.S. Pat. No. 3,584,520, in the case of a hydrodynamic torque converter, that a centric bearing sleeve is attached by its one front end to a radial connecting face of a hub and is joined to the latter by a fillet weld, with the hub being situated radially inside of the outer shell of a pump impeller and being configured in one piece with this outer shell.
According to German Journal: "Schwei.beta.en und Schneiden", Year 20 (1968), Issue 11, tough competition with domestic and foreign industry is constantly forcing motor-vehicle manufacturers to check new technological developments to see whether they might contribute, within the framework of large-scale production, to solving existing technical problems and to achieving more economical working methods. Since friction welding, as a joining process for butt seams, reportedly offers some basic production-engineering and welding advantages over joining methods previously used in a number of motor vehicle parts, it would already have been used in the motor vehicle shortly after its development to practical maturity. Among a selection of applications, this publication shows an impeller of a recirculating positive-displacement pump. According to the publication, friction welding can also be used in the production of a splined shaft. The separate manufacture of a pipe part having inner grooves and the connection of the finished piece to the other shaft part make it substantially easier for grooves to be introduced in the bore.
According to Eichhorn/Borowka "Schwei.beta.en und Schneiden", VDI-Journal, Vol. 128 (1986), No. 20--October (II), p. 806, the suitability also of turbine blades, turbine wheels and runner rims to flywheel welding is proven. In overall terms, it is not only for the manufacture of high-precision, safety-related structural parts that friction welding has reportedly proved its worth.
Finally, it is known that the joint parts should have at the abutment points, where possible, the same cross-sections. The joining of parts having unequal abutment point cross-sections could be carried out, without difficulties, in the same way as welding bolts or pipes onto metal plates.
An object of the present invention is to provide a friction-welding process and apparatus which ensure usability by preventing a disruptive burr without expensive added complexity.
The foregoing object has been achieved according to the present invention by a process wherein a geometric end shape of the weld bead following completion of the upsetting procedure is defined by a form tool, which is respectively disposed immovably in the direction of the rotational axis relative to the one receiving fixture such that relative to the bonding zone, the plastic material forced out of the bonding zone during the upsetting procedure is brought into the end shape, without cutting, by a form face of the form tool, no later than completion of the upsetting procedure.
In the process according to the present invention, the weld bead is shaped during the welding procedure such that usability is obtained without any subsequent working, because there is no longer any possibility of a disruptive burr being present. A joint-part preparation with the intention of facilitating the deformation of the still warm weld bead, for the prevention of the welding burr, is obtainable.
Where the process according to the present invention is applied to friction welding in order to join end faces of a centric bearing sleeve and of a coaxial, single-part connecting branch, belonging to a radially inner hub configured in one piece with an outer shell of a pump impeller of a hydrodynamic torque converter, a special joint-part preparation is able to be relinquished. This is because the weld bead, which has formed at the transition of the end faces, joined together by welding, into the respectively axially adjoining outer contacting surface, is at least partially expelled in the direction of the transition between the hub and the connecting branch.
The present invention also relates to apparatuses for realizing the novel process of the present invention such that the weld bead is shaped advantageously during the welding procedure.
In the process according to the invention, upon completion of the welding procedure, when the weld bead is deformed during cooling of the bonding zone, a situation can be reached, due to the still revolving rotary-driven receiving fixture and the temperature cycle of the friction-welding machine, in which the coaxiality of the two receiving fixtures in relation to the rotational axis is abolished. This coaxiality error is all the greater, the more elastic is the machine frame between the two receiving fixtures.
Other aspects of the process according to the present invention focus upon preventing the described coaxiality errors.